<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>Three.js - PreserveDrawingBuffer</title>
    <style>
    html, body {
        height: 100%;
        margin: 0;
    }
    #c {
        width: 100%;
        height: 100%;
        display: block;
    }
  </style>
  </head>
  <body>
    <canvas id="c"></canvas>
  </body>
<script type="importmap">
{
  "imports": {
    "three": "../../build/three.module.js"
  }
}
</script>

<script type="module">
import * as THREE from 'three';

function main() {

	const canvas = document.querySelector( '#c' );
	const renderer = new THREE.WebGLRenderer( {
		canvas,
		preserveDrawingBuffer: true,
		alpha: true,
		antialias: true
	} );
	renderer.autoClearColor = false;

	const camera = new THREE.OrthographicCamera( - 2, 2, 1, - 1, - 1, 1 );

	const scene = new THREE.Scene();

	{

		const color = 0xFFFFFF;
		const intensity = 3;
		const light = new THREE.DirectionalLight( color, intensity );
		light.position.set( - 1, 2, 4 );
		scene.add( light );

	}

	const boxWidth = 1;
	const boxHeight = 1;
	const boxDepth = 1;
	const geometry = new THREE.BoxGeometry( boxWidth, boxHeight, boxDepth );

	const base = new THREE.Object3D();
	scene.add( base );
	base.scale.set( 0.1, 0.1, 0.1 );

	function makeInstance( geometry, color, x, y, z ) {

		const material = new THREE.MeshPhongMaterial( { color } );

		const cube = new THREE.Mesh( geometry, material );
		base.add( cube );

		cube.position.set( x, y, z );

		return cube;

	}

	makeInstance( geometry, '#F00', - 2, 0, 0 );
	makeInstance( geometry, '#FF0', 2, 0, 0 );
	makeInstance( geometry, '#0F0', 0, - 2, 0 );
	makeInstance( geometry, '#0FF', 0, 2, 0 );
	makeInstance( geometry, '#00F', 0, 0, - 2 );
	makeInstance( geometry, '#F0F', 0, 0, 2 );

	function resizeRendererToDisplaySize( renderer ) {

		const canvas = renderer.domElement;
		const width = canvas.clientWidth;
		const height = canvas.clientHeight;
		const needResize = canvas.width !== width || canvas.height !== height;
		if ( needResize ) {

			renderer.setSize( width, height, false );

		}

		return needResize;

	}

	const state = { x: 0, y: 0 };

	function render( time ) {

		time *= 0.001; // convert to seconds

		if ( resizeRendererToDisplaySize( renderer ) ) {

			const canvas = renderer.domElement;
			camera.right = canvas.clientWidth / canvas.clientHeight;
			camera.left = - camera.right;
			camera.updateProjectionMatrix();

		}

		base.position.set( state.x, state.y, 0 );
		base.rotation.x = time;
		base.rotation.y = time * 1.11;

		renderer.render( scene, camera );

		requestAnimationFrame( render );

	}

	requestAnimationFrame( render );

	function getCanvasRelativePosition( event ) {

		const rect = canvas.getBoundingClientRect();
		return {
			x: ( event.clientX - rect.left ) * canvas.width / rect.width,
			y: ( event.clientY - rect.top ) * canvas.height / rect.height,
		};

	}

	const temp = new THREE.Vector3();
	function setPosition( e ) {

		const pos = getCanvasRelativePosition( e );
		const x = pos.x / canvas.width * 2 - 1;
		const y = pos.y / canvas.height * - 2 + 1;
		temp.set( x, y, 0 ).unproject( camera );
		state.x = temp.x;
		state.y = temp.y;

	}

	canvas.addEventListener( 'mousemove', setPosition );
	canvas.addEventListener( 'touchmove', ( e ) => {

		e.preventDefault();
		setPosition( e.touches[ 0 ] );

	}, { passive: false } );

}

main();
</script>
</html>
